While conventional brush-commutated DC motors may have advantageous characteristics, including convenience of changing operational speeds, there may be disadvantages such as brush wear, electrical loss, noise and radio frequency interference caused by sparking between the brushes and the segmented commutator, which may limit the applicability of such brush-commutated DC motors in some fields such as the vehicular blower control field. Electronically commutated motors, such as brushless DC motors and permanent magnet motors with electronic commutation, have now been developed and generally are believed to have the above-discussed advantageous characteristics of the brush-commutated DC motors without many of the disadvantages thereof while also having other important advantages. Such electronically commutated motors are disclosed in the David M. Erdman U.S. Pat. Nos. 4,015,182 and 4,459,519 for instance. These electronically commutated motors are advantageously employed, for instance, commutated motors in air conditioning for cooling and warming of vehicular compartments.
In an automotive temperature control system a variable resistance can be used to vary the speed of a brush-type blower motor, but this would further reduce the energy efficiency of the system. While there are some losses engendered by electronic switching of an electronically commutated motor, these are negligible compared to brush losses and rheostat losses in prior art variable speed blower systems.
Further improvements in control systems, electronically commutated motor systems, blower apparatus and methods of control and operation can beneficially contribute to more widespread use of such motors in various applications including vehicular blower control. For example, sudden changes in the blower speed control setting can lead to wasted electrical energy due to an inrush current to the motor and produce annoying air sounds as the operating level is changed. Improvements which achieve increased electrical efficiency and user convenience would be desirable. Economy of manufacture would also be enhanced by circuit improvements if they can be made with little extra cost as part of improved integrated circuit chips. Greater versatility of response to various control signal conditions and improved fail-safe features would also be desirable.
The control circuitry required to electronically commutate a brushless DC motor is typically mounted remote from the motor in a location where the circuitry can be adequately cooled and unaffected by motor heat. In applications where the control circuitry is mounted on or in proximity to the motor, a dedicated cooling mechanism such as a fan wheel is generally employed to provide the required heat dissipation, i.e., the mechanism is provided primarily for the purpose of cooling the control circuitry. Alternatively, in applications where the motor is part of a blower cooling system, the control circuitry may be mounted on a printed circuit board on the stator and cooled by air moved by the blower assembly. In the former case, the dedicated cooling mechanism results in additional cost and failure of such mechanism results in added maintenance expenses. In the latter case, the control circuitry may not be sufficiently cooled and may not be accessed for repair or maintenance without disassembly of the motor.